(x+2y-3)(x-2y-3)=[(x-3)+2y]*[(x-3)-2y]
(x+y)²(x-y)²-(x-y)(x+y）(x²+y²)
=(x^2-y^2)^2-(x^2-y^2)(x^2+y^2)
=(x^4-2x^2 *y^2+y^4)-(x^4-y^4)
=-2x^2*y^2+2y^4
数学问题--------平方差公式&完全平方公式
(x+2y-3)(x-2y-3)=[(x-3)+2y]*[(x-3)-2y]
(x+y)²(x-y)²-(x-y)(x+y）(x²+y²)
=(x^2-y^2)^2-(x^2-y^2)(x^2+y^2)
=(x^4-2x^2 *y^2+y^4)-(x^4-y^4)
=-2x^2*y^2+2y^4